Electrocatalytic oxygen reduction on nitrogen-doped graphene in alkaline media

Abstract

Nitrogen-doped graphene nanosheets were prepared from nitrogen precursor and graphene oxide (GO), which was synthesised from graphite by modified Hummers’ method. Melamine, urea and dicyandiamide (DCDA) were used as nitrogen precursors and the doping was achieved by pyrolysing GO in the presence of these nitrogen-containing compounds at 800°C. The N-doped graphene (NG) samples were characterised by scanning electron microscopy and X-ray photoelectron spectroscopy, the latter method revealed successful nitrogen doping. The oxygen reduction reaction (ORR) was examined on NG-modified glassy carbon (GC) electrodes in alkaline media using the rotating disk electrode (RDE) method. It was found on the basis of the RDE results that nitrogen-containing catalysts possess higher electrocatalytic activity towards the ORR than the annealed GO. Oxygen reduction on this GO material and on NG catalysts prepared by pyrolysis of GO-melamine and GO-urea followed a two-electron pathway at low overpotentials, but at higher cathodic potentials the desirable four-electron pathway occurred. For NG catalyst prepared from GO-DCDA a four-electron O2 reduction pathway dominated in a wide range of potentials. The half-wave potential of O2 reduction on this NG catalyst was close to that of Pt/C catalyst in 0.1M KOH. These results are important for the development of alkaline membrane fuel cells based on non-platinum cathode catalysts.